Adding insulation to attic, no vapor barrier

[wedge40]

This is hilarious. I've read every reply and I'm pretty sure right now it's about 50-50 vapor barrier or no vapor barrier. I bet if you ask local contractors you will get the same mix.
I'm in the same boat. My attic has 4"-6" of blown in insulation, no vapor barrier between dry wall and rafters. It's well ventilated and I plan on just getting UNFACED bats and put them perpendicular to the rafters. Is this perfect.. Heck no!!! But it will be way better then what I have right now.

Wedge

 

[SPYDERLK]

I would not vapor barrier the rafters ... only the ceiling between. The rafter bottoms are exposed to the ceiling and will dampen. Let the rafters breathe so they can let that moisture go.
larry

 

[Reverend Blair]

This is hilarious. I've read every reply and I'm pretty sure right now it's about 50-50 vapor barrier or no vapor barrier. I bet if you ask local contractors you will get the same mix.
I'm in the same boat. My attic has 4"-6" of blown in insulation, no vapor barrier between dry wall and rafters. It's well ventilated and I plan on just getting UNFACED bats and put them perpendicular to the rafters. Is this perfect.. Heck no!!! But it will be way better then what I have right now.

Wedge

I think a lot of that is the difference between old and new technologies, Wedge. New codes require vapour barriers in most places. There are a few reasons for that.

The first is lifestyle. We shower every day now. We cook differently and eat different foods, putting more moisture in the air. We keep the temperature higher in the winter.

The second is technological. Our windows and doors are better, we use latex paint instead of oils, we insulate with different materials, and those materials become much less effective if they get wet.

The bit about not having a vapour barrier so the house can "breathe" is about the same as saying a punctured lung is a good thing though. A house should breathe the same way you do...through the prescribed orifices.

 

[dmccarty]

A vapor barrier might be required in a northern climate but that same vapor barrier in the south could cause problems. Do NOT build or rehab a house based on construction details from a climate different than yours. It is asking for trouble.

I designed our house based on the construction details in Joseph Lstiburek's "Builders Guide to Mixed Climates." Lstiburek has books on four different building climates. It looks like your area is considered a Mixed Climate.

His design specs DO NOT use vapor barriers like plastic sheeting as a vapor barrier. He specs a semi vapor permeable barrier for the walls and ceiling aka latex paint.

Here is link to his website regarding vapor barriers. His website also sells his books if you think you need them. You can likely find the details you need in the link below or by searching the website. Just make sure you follow the details for your climate.

Vapor Barrier Guidance — Building Science Information

I need to run some coax and Cat 5 wire over the holidays so I brought my breathing mask to the house so I can use it in the attic. This is not a n95 mask but one with canisters on it. It works much better than the N95 masks at filtering gunk out of the air AND allowing you to breath while working. The attic air is not that dusty but our old city house was really nasty up in the attic. I was up in the attic a week or so ago without a mask. Not bad but I still was coughing a bit.

We do have blown in insulation with some batt. If I was going to add blown insulation and it your case that seem the thing to do I would get/wear a good quality mask.

Later,
Dan

 

[kenstrac]

Before you do anything have someone check what the roof will withstand with a snow load,and with the weird weather we have been having lately I would be looking for a higher number.
Old houses were built with little or no insulation,in some instances around here they could not insulate to present standards or the roof would have collapsed.

 

[buckeyefarmer]

A call to your local insulation contractor would be a good thing. They usually have good prices and can do a much better job than you can. They furnish and install insulation for about what you can by it for. They already know the codes, and they probably will have ideas that you had not even thought of. You'll know the vapor barrier in your attic is working when condensation runs down the inside of your windows in cold weather and mold starts growing in dark places.

When I built one of the things I sub contracted was the insulation. they supplied and did the job cheaper that I could buy the insulation. However, they also did a cheaper job. They did not put in the proper sized air vents (12" for 16" spaces), missed insulation in some places, and in general did not install it as well as I would have liked. However, they did it in one day, and it would have taken me a week doing it myself. I have a lot of air that gets blown into my front attic spaces, and consequently into my upstairs living space by air leaking around the insulation.

 

[Craig Clayton]

I went to This Old House for vapour barrier references.
How to Insulate an Attic | Video | Insulation | This Old House
I did not watch it all the way through but these gentlmen know the facts.
Craig Clayton

 

[jonyyuma]

I went to This Old House for vapour barrier references.
How to Insulate an Attic | Video | Insulation | This Old House
I did not watch it all the way through but these gentlmen know the facts.
Craig Clayton

Interesting, watched it to the end. Poly is approved by them, but not in solid sheet across the beams? .Jy.

 

[bdeboer]

This is hilarious. I've read every reply and I'm pretty sure right now it's about 50-50 vapor barrier or no vapor barrier. I bet if you ask local contractors you will get the same mix.
Wedge

I think the mix is divided 50-50 between Canada and the States. Somewhat due to local codes. I personnally would go the vented soffit/ridge with insulation bafflles and not add plastic due to mold between the plastic and the sheet rock concerns. Also caulk/foam electrical boxes etc. that penatrate the drywall. This is in our Central Ohio climate where our temperatures run from 0 deg. F to 95 deg. F depending on the season.

See the DMcCarty post and read the Building Sciences website before making your decision.

Another thing to do would be to crawl around your attic on a cold day and feel for heat escaping. I would check the top of interior walls etc. if you have balloon framing. Block these openings with something that won't burn easiliy.

 

[Jimmy Joe]

I went to This Old House for vapour barrier references.
How to Insulate an Attic | Video | Insulation | This Old House
I did not watch it all the way through but these gentlmen know the facts.
Craig Clayton

Seems like there would be plenty of chance for moisture to get in the attic by just stuffing the insulation between the joists like that, not a tight fitting vapor barrier.